1. Field of Invention
This invention is related to the polymerization and curing of ethylenically unsaturated monomers and of methyl methacrylate-containing syrups. More particularly, it is related to the improved, more rapid production of articles of polymeric methyl methacrylate, e.g., methacrylate homopolymer and copolymers of methyl methacrylate with alpha,beta-ethylenically unsaturated compounds such as vinyl acetate, styrene, alkyl acrylates, alkyl methacrylates, and the like.
2. Description of Prior Art
In the production of articles of polymeric methyl methacrylate and, more specifically, in the curing or polymerization of the monomers involved for producing the polymeric articles, the most important step is the curing of the methyl methacrylate-containing syrup. For this step it is necessary to use a catalyst or, as it is sometimes called, an initiator. As catalysts, the prior art has suggested the use of peroxy compounds such as lauroyl peroxide and benzoyl peroxide. Recently, the use of the hemi-perester of maleic acid has been disclosed as a useful catalyst for the polymerization and curing of methyl methacrylate-containing syrups. However, it is known that, although this catalyst is quite effective, it operates rather slowly. Thus, curing times of over four hours are not uncommon in the preparation of articles of the methyl methacrylate homopolymer when curing at or near room temperature.
The rate of curing of such methyl methacrylate-containing syrups has been increased through the use of metal salts of the hemi-peresters of maleic acid as disclosed in U.S. Pat. No. 3,362,942, issued Jan. 9, 1968 to George E. Munn. However, even this catalyst requires 1-2 hours to complete the polymerization and curing. When a mercaptan activator is included in the syrup, the curing rate can be further increased but the curing step still requires 15-20 minutes for thick sheets and the activator's high cost is disadvantageous.